Neural network modelling for mean velocity and turbulence intensities of steep channel flows     

Fi‐John Chang  Han‐Chung Yang  Jau‐Yau Lu  Jian‐Hao Hong 《水文研究》2008,22(2):265-274

The main purpose of this study is to evaluate the potential of simulating the profiles of the mean velocity and turbulence intensities for the steep open channel flows over a smooth boundary using artificial neural networks. In a laboratory flume, turbulent flow conditions were measured using a fibre‐optic laser doppler velocimeter (FLDV). One thousand and sixty‐four data sets were collected for different slopes and aspect ratios at different locations. These data sets were randomly split into two subsets, i.e. training and validation sets. The multi‐layer functional link network (MFLN) was used to construct the simulation model based on the training data. The constructed MFLN models can almost perfectly simulate the velocity profile and turbulence intensity. The values of correlation coefficient (γ) are close to one and the values of root mean square error (RMSE) are close to zero in all conditions. The results demonstrate that the MFLN can precisely simulate the velocity profiles, while the log law and Reynolds stress model (RSM) are less effective when used to simulate the velocity profiles close to the side wall. The simulated longitudinal turbulence intensities yielded by the MFLN were also fairly consistent with the measured data, while the simulated vertical turbulence intensities by the RSM were not consistent with the measured data. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Analytical solutions for a three‐invariant Cam clay model subjected to drained loading histories     

Dunja Peri&#x; 《国际地质力学数值与分析法杂志》2006,30(5):363-387

Analytical solutions are derived for a three‐invariant Cam clay model subjected to proportional and circular drained loading histories. The solutions are presented for a specific volume, and volumetric and generalized shear strains. In the case of a proportional loading only straight effective stress paths are considered while in the case of a circular loading the maximum possible change in Lode's angle is π/3 due to plastic isotropy. Additionally, a concept of deviatoric stiffness is devised and an analytical expression for the generalized hardening modulus is derived. Qualitative and quantitative analyses are carried out in the form of direct comparisons between analytical solutions for drained and undrained loading histories thus offering an improved understanding of the three‐invariant model. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Patterns in stream longitudinal profiles and implications for hyporheic exchange flow at the H.J. Andrews Experimental Forest,Oregon, USA     

Justin K. Anderson  Steven M. Wondzell  Michael N. Gooseff  Roy Haggerty 《水文研究》2005,19(15):2931-2949

There is a need to identify measurable characteristics of stream channel morphology that vary predictably throughout stream networks and that influence patterns of hyporheic exchange flow in mountain streams. In this paper we characterize stream longitudinal profiles according to channel unit spacing and the concavity of the water surface profile. We demonstrate that: (1) the spacing between zones of upwelling and downwelling in the beds of mountain streams is closely related to channel unit spacing; (2) the magnitude of the vertical hydraulic gradients (VHGs) driving hyporheic exchange flow increase with increasing water surface concavity, measured at specific points along the longitudinal profile; (3) channel unit spacing and water surface concavity are useful metrics for predicting how patterns in hyporheic exchange vary amongst headwater and mid‐order streams. We use regression models to describe changes in channel unit spacing and concavity in longitudinal profiles for 12 randomly selected stream reaches spanning 62 km² in the H.J. Andrews Experimental Forest in Oregon. Channel unit spacing increased significantly, whereas average water surface concavity (AWSC) decreased significantly with increasing basin area. Piezometer transects installed longitudinally in a subset of stream reaches were used to measure VHG in the hyporheic zone, and to determine the location of upwelling and downwelling zones. Predictions for median pool length and median distance between steps in piezometer reaches bracketed the median distance separating zones of upwelling in the stream bed. VHG in individual piezometers increased with increasing water surface concavity at individual points in the longitudinal profile along piezometer transects. Absolute values of VHG, averaged throughout piezometer transects, increased with increasing AWSC, indicating increased potential for hyporheic exchange flow. These findings suggest that average hyporheic flow path lengths increase—and the potential for hyporheic exchange flow in stream reaches decreases—along the continuum from headwater to mid‐order mountain streams. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

教改是提高大学生就业率的关键环节   总被引：1，自引：0，他引：1  

时新荣 《成都信息工程学院学报》2006,21(5):744-750

从当前我国人力资源市场上大学生就业难的现象切入，通过分析大学生就业市场供求双方的经济关系，说明求职大学生在素质上与用人单位的需求之间存在较尖锐的矛盾，是大学生就业难的重要原因。解决大学生就业难的关键环节之一是通过教改提高大学生的综合素质。  相似文献   

Orientation of Sandhoppers Under Natural Conditions in Repeated Trials: an Analysis Using Longitudinal Directional Data     

A. D'elia  C. Borgioli  F. Scapini   《Estuarine, Coastal and Shelf Science》2001,53(6):839

Zonal recovery is a prompt escape towards the sea performed by sandhoppers under stressful environmental conditions. Differences in habitat features, meteorological conditions during the tests and morphological characteristics of the individuals are all factors affecting orientation. This paper deals with the temporal variation of the orientation of a sandhopper sample, taking into account the effect of some environmental and morphological variables on these changes. The directions chosen by single animals in repeated trials under natural conditions were analysed, using longitudinal circular data. The longitudinal analysis highlights several details about three different kinds of intrapopulation variation due to: sun, wind and eye left/right asymmetry. A clear link between the successive directional responses is demonstrated as well as modulation of behaviour with time: the animals stabilise orientation towards a certain direction in successive trials. The use of longitudinal sets of data in orientation studies produces a good synthesis of directional behaviour, due to several advantages of this kind of analysis. These include the fact that the association between successive behaviours and variability through repeated trials is taken into account; a progressive improvement, due to the integration of information from previous experiences, can be detected; the role of the main cues and factors affecting orientation is more accurately defined; and more parsimonious statistical models can be used to fit the data.  相似文献   

基于自适应分组的预警信息发布系统     

徐冬卫  沈晓东  陈苏婷 《南京气象学院学报》2013,5(1):73-76

介绍了DAB(数字音频广播)主业务信息通道的传输结构及其作用,提出了一种应用于DAB发射机在主业务信息通道传输文字模块的设计方案.该设计针对现有DAB发送文字信息所需的多样性、实时性和经济性的要求,基于MOT(多媒体对象传输)协议传输规范,利用自适应分组模式传输机制提高了DAB发射系统发送文本信息(气象预警信息、交通信息等)的灵活性和子信道容量的利用率.该方案已通过自适应分组编码软件实现.  相似文献   

济南双偏振多普勒天气雷达在线自动标定数据质量分析评估          下载免费PDF全文

杨传凤  刁秀广  张骞  魏海文 《山东气象》2020,40(4):114-123

阐述了CINRAD/SA-D双偏振多普勒天气雷达（简称“双偏振雷达”）标定技术,统计分析了济南双偏振雷达试运行以来在线自动标定数据和该时间段内的维护维修情况,从雷达几十个标定状态性能参数中,遴选对雷达探测数据质量影响最大的发射峰值功率Pt、相位噪声σφ、噪声系数NF、反射率标定系数SYSCAL、差分反射率因子ZDR、差分传播相移ΦDP等性能参数,分析评估在线自动标定数据质量。结果表明：1）峰值功率维持在679.68 kW,H（水平）和V（垂直）双通道的峰值功率长期运行吻合一致性较好。2）H和V双通道噪声系数均值分别维持在1.66 dB和1.73 dB,双通道数据总体分布稳定,且具有较好的一致性;标定数据的异常来源于外界干扰,占0.39%,受外界干扰H通道多于V通道,干扰造成接收机灵敏度降低了1.5 dB,导致雷达产品异常。3）反射率标定ΔSYSCAL最小值为-0.46 dB,最大值为0.25 dB,满足±2 dB的技术指标要求。4）I/Q相角法标定相位噪声均值为0.051 3°,实物对消能力60 dB与估测地物杂波抑制能力61.36 dB结果基本吻合,证实了雷达系统具有较好的地物杂波抑制能力。5）采用机内CW、TS双信号源标定法,接收双通道幅度和相位的标准差：ZDR-CW和ΦDP-CW分别为0.025 dB和0.735,ZDR-TS和ΦDP-TS分别为0.044 dB和1.116°,满足接收双通道一致性的技术指标,但CW信号标定结果明显小于TS信号标定结果,表明双路方位旋转关节对接收链路信号幅度和相位的一致性有影响,导致ZDR-TS和ΦDP-TS标定结果比ZDR-CW和ΦDP-CW出现更大的偏差,因此随着双偏振雷达的长期运行,对方位旋转关节带来的幅度和相位固有偏差进行测试和订正非常重要。  相似文献   

遥感线性构造分形统计和蚀变信息提取在桂东地区金铅锌锡多金属成矿预测中的应用   总被引：2，自引：1，他引：1  

赵少杰  钱建平  陈宏毅 《大地构造与成矿学》2011,35(3):364-371

在桂东地区ETM+遥感影像742波段融合的基础上,进行了线性构造和环形构造解译,运用分形几何学的原理和方法对研究区的遥感线性构造进行定量分析,利用计盒维数法求得研究区的线性构造分维值,得出该区线性构造具有良好的统计自相似性和分形特征,利用Surfer软件求得线性构造分维等值线图,采用主成分分析和比值法组合提取遥感蚀变异...  相似文献   

瞬变电磁法圆形线圈自感计算     

武中华  李文尧  简燕 《物探化探计算技术》2011,33(6):596-600,572

在瞬变电磁法（TEM）中,圆形回线的自感参数用于局部导体晚期瞬变电磁场的等效计算、接收线圈固有过渡过程计算、关断时间的计算以及瞬变电磁仪器研制等。目前,在瞬变电磁法教科书中,圆形线圈自感计算均使用近似公式。这里根据毕奥-萨伐尔定律推导出单匝圆形线圈磁感应强度及自感的积分表达式,利用MATLAB软件进行数值计算。结果表明,目前使用的自感近似公式,在用于计算半径为0.5 m和1 m的圆形接收回线自感时,误差分别为-18.978%和-26.542%。用于计算发射回线的自感时,当回线半径从2.821 0 m～112.837 9 m时,自感近似公式的误差从-35.84%～-55.65%,且单匝正方形回线与等面积单匝圆形回线的自感值之间存在5.12%～8.11%的偏差。  相似文献   

含不同半径孔洞的颗粒体模型的力学行为数值模拟   总被引：3，自引：0，他引：3  

伍小林  王学滨  潘一山 《中国地质灾害与防治学报》2011,22(1):107-114

本文通过编程建立了非连续介质(颗粒体材料)模型,采用FLAC软件模拟了静水压力条件下不同半径的巷道围岩中的剪切应变增量、最小主应力及最大主应力的分布规律。研究表明,随着孔洞半径的增大,呈圆环形的剪切应变增量与最小主应力的高值区的圈数、呈辐射状的最大主应力的高值区的延伸范围及剪切应变增量的最大值都呈先慢后快的增长趋势。模型中最大的拉应力接近于在模型四周所施加的压应力,而最大的压应力约为所施加的压应力的5～10倍。模型内部的剪切应变增量、最小主应力及最大主应力的分布是高度不均匀的。具有较高的差应力的位置与具有较高的剪切应变增量的位置具有很好的一致性。  相似文献